Abstract. Nanocomposite hydrogels based on poly(vinyl alcohol) -PVA and sepiolite have been prepared and their potential for drug delivery systems has been assessed by taking rifampicin as model drug. The nanocomposite hydrogels were characterized by WAXS and DSC and the swelling behavior and structural stability were evaluated. The effect of the presence of rifampicin, sepiolite and simultaneous rifampicin-sepiolite on the structure and swelling of the hydrogels was investigated. The swelling data were analyzed in order to evaluate the diffusion mechanisms of water. The results indicate that both rifampicin and sepiolite cause important modifications on microstructure of the PVA matrix, leading to changes on swelling and diffusional behavior.

A comparative study of the development of nitrile rubber (NBR) based nanocomposites was performed; two organomontmorillonites (Cloisite 15A and Cloisite 30B) and two procedures for clay dispersion (melt blending and solution intercalation) were used. The nanocomposites were cured with a system based on dicumyl peroxide in the presence of m-phenylenebismaleimide as a coagent for curing. The dispersion of the organoclay inside the NBR matrix was investigated with transmission electron microscopy and X-ray diffraction. All the cured systems displayed a combination of intercalated, partially exfoliated clay platelets and confined, deintercalated clay; the degree of dispersion depended on the amount of clay, the type of intercalant, and the intercalation procedure. The highest amount of intercalated/exfoliated clay was obtained with a previous dispersion of the clay (Cloisite 30B) in an NBR solution. All the nanocomposites presented outstanding tensile strength and creep response, and this indicated a reinforcing effect of the layered silicates.

NBR/PA6 blends were prepared at the melt state and with the use of masterbatches. Compatibilization with NBR-oxazoline was tested with the aim of enhancing the blend performance and to obtain more appropriated morphology. The effect of compatibilizer content was studied through the characterization of blend mechanical properties, creep behavior, swelling, PA6 phase crystallinity, morphology, and rheological properties, including pressure-volume-temperature behavior. The results show a more significant elastomeric behavior for blends with 5 and 7 phr of compatibilizer, with deleterious effects for higher content. The migration of compatibilizer into elastomeric phase was documented by electronic microscopy, and corroborated by an increase in free volume of the samples.

Summary: The reactive compatibilization of ethylene‐propylene‐diene (EPDM)/nitrile rubber (NBR) blends was performed using mercapto‐modified copolymers (mercapto‐modified EPDM, EPDMSH, and mercapto‐modified ethylene‐vinyl acetate copolymer, EVASH) in combination with oxazoline‐functionalized NBR (NBR‐ox). The best mechanical performance was achieved with the two EVASH‐based compatibilizing systems, especially the one containing the co‐reactive copolymers because of the reactivity of the oxazoline group. The presence of insoluble material in non‐vulcanized blends suggested the reactive compatibilization. The morphologies of these blends were examined through scanning electron microscopy (SEM). Blends compatibilized with the EVASH‐based systems showed finer morphologies than the non‐compatibilized blend or those compatibilized with the EPDMSH‐based systems. In non‐vulcanized NBR/EPDM (70:30 wt.‐%) blends, the presence of the co‐reactive EVASH/NBR‐ox system changes the morphology from a cocontinuous structure towards a droplet‐matrix morphology, and also results in a significant broadening of the damping curve related to the NBR transition, observed from DMTA analysis. The effect of the compatibilization on aging resistance has also been evaluated.SEM micrograph of a non‐vulcanized NBR/EPDM blend compatibilized with a NBR‐ox/EVASH co‐reactive copolymer.magnified imageSEM micrograph of a non‐vulcanized NBR/EPDM blend compatibilized with a NBR‐ox/EVASH co‐reactive copolymer.

turas elevadas e resistência química. Borracha nitrílica, por sua vez, é um elastômero para propósitos especiais, devido à sua ótima resistência a óleo e a abrasão [4][5][6][7] . Supõe-se que a combinação de tais componentes pode gerar um material com boa resistência a óleo quente e boas propriedades mecânicas, particularmente a altas temperaturas [8,9] . Apesar do potencial, pouco se tem publicado em relação a misturas de PA6 e NBR, provavelmente devido à alta temperatura necessária para o processamento e moldagem do PA6, que pode causar a degradação do elastômero. Nosso grupo de pesquisa estudou a incorporação de aditivos a fim de melhorar a processabilidade e as propriedades finais da mistura [10] . O teste de fluência ("creep") é um ensaio mecânico importante ao simular deformações que podem ocorrer duran- IntroduçãoElastômeros termoplásticos vulcanizados ("thermoplastic elastomers vulcanized" -TPV) são materiais altamente promissores devido às suas características de multi-aplicabilidade e reprocessabilidade [1,2] . TPV's unem a processabilidade dos termoplásticos com a elasticidade dos elastôme-ros em um único material. Dentre os vários tipos de TPV, a mistura polimérica tem maior potencial de aplicabilidade devido à ampla gama de materiais que podem ser combinados. O meio mais comum de se obter um TPV através de misturas é a vulcanização dinâmica da fase elastomérica, descrita pela primeira vez por Gessler e colaboradores [3] . Poliamidas são termoplásticos com elevado módulo, resistência mecânica, estabilidade dimensional a tempera- Resumo: Os materiais testados neste trabalho são o resultado de um estudo do uso de aditivos e compatibilizantes na mistura de poliamida 6 (PA6) e borracha nitrílica (NBR), realizado com o objetivo de melhorar suas propriedades mecânicas e facilitar o processamento da mistura. Fluência ("creep") é um teste mecânico importante ao simular a aplicação final do material de engenharia, possibilitando a previsão do desempenho de modo comparativo. Entretanto, é um teste pouco explorado na caracterização de TPV's. A melhora nas propriedades com a adição de aditivos e a eficiência do processo de compatibilização pode ser observada através da variação na compliância das amostras analisadas. Os resultados são correlacionados usando testes de densidade, teor de gel, resistência à tração e microscopia eletrônica de varredura. O presente trabalho mostra que é possível avaliar um material em condições semelhantes à aplicação final em um teste rápido e com gasto mínimo de material. Palavras-chave: PA6, NBR, TPV, propriedades mecânicas, fluência. Creep Behavior of Polyamide 6/Nitrylic Rubber TPV's BlendsAbstract: The materials tested in this work are the result of a study involving the use of additives and compatibilization in blends of PA6 and NBR, which was aimed at enhancing the mechanical properties and processability of the blend. Creep is an important mechanical test since it simulates the final application of the material, allowing a prediction of material performance, in a comparative...